A voltage-driven element is an element capable of performing a specific function using a driving voltage, and is widely used in various applications. In an example of the voltage-driven element, a voltage-driven switching element comprising an insulated gate is known. The voltage-driven switching element controls a current value based on a gate voltage (an example of the driving voltage) supplied to the insulated gate, and is used, e.g., in an inverter system that converts a direct current voltage to an alternating current voltage. A power semiconductor switching element that includes an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be given as an example of the voltage-driven switching element.
In order to drive this type of the voltage-driven element, a drive unit is connected to the voltage-driven element. The drive unit is configured to control the driving voltage supplied to the voltage-driven element. For example, the drive unit can control the driving voltage based on a control signal that commands on/off of the voltage-driven element. The drive unit can also control the driving voltage based on a signal representing a driving state of the voltage-driven element, or a signal representing a state of the external environment.
As a driving method of such drive unit, a technique referred to an active gate driving method has been developed. The active gate driving method is characterized in that a driving condition relating to the driving voltage is changed during a transitional period between a driving state and a non-driving state of the voltage-driven element to improve both of a surge voltage and a switching loss. For example, when the voltage-driven element transits from the off-state to the on-state, one active gate driving method may be carried out such that a gate resistance is set to be high at an anterior half of the transitional period to make an ascent rate of the driving voltage be low and the gate resistance is set to be low at a later half of the transitional period to make the ascent rate of the driving voltage be high. Alternatively, when the voltage-driven element transits from the off-state to the on-state, another active gate driving method may be carried out such that the driving voltage is set to be low at the anterior half of the transitional period and the driving voltage is set to be high at the later half of the transitional period. Examples of such active gate driving methods are disclosed in JP App. Pub. No. 2010-022190, JP App. Pub. No. 2001-314075 or JP App. Pub. No. H10-23743.